Parallel VFD Control via Speed Droop and Flux Share
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Solution Overview
Problem
Existing systems for parallel control of variable frequency drives are complex and expensive due to the need for high communication rates and master-slave configurations, which complicate the control of multiple drives and increase costs.
Innovation Solution
A system with a master controller and independent variable frequency drives, each equipped with a speed droop module and a flux share module, communicates at a lower data rate to regulate torque and magnetizing current components, allowing for simpler and less expensive parallel control by determining motor speed and flux based on stator voltage and current measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a master-slave configuration is used for parallel control of variable frequency drives, then the power requirement of the load can be met, but the control complexity and cost increase due to high communication rates and master-slave arrangements
Solution Approach 1:
The patent divides the control functions into two independent segments: speed regulation (handled by speed droop module) and flux regulation (handled by flux share module). Each variable frequency drive operates independently with its own complete control circuit, eliminating the need for master-slave hierarchy and high-speed communication between drives.
Solution Approach 2:
The patent changes the control parameters from traditional master-slave current commands to decentralized speed droop and flux share parameters. By using speed droop characteristics and magnetizing current sharing, the system achieves parallel operation without requiring complex communication protocols or synchronized control.
2Power
If a master-slave configuration is used for parallel control of variable frequency drives, then the power requirement of the load can be met, but the communication cost and data rate requirements increase
Solution Approach 1:
The patent extracts the high-speed communication requirement from the parallel control system. By implementing independent speed droop and flux share control, the system eliminates the need for high-rate communication between drives, reducing communication to standard control signals only.
3Productivity
If traditional parallel control methods are used, then multiple drives can operate together, but the dynamic performance and response time are compromised due to communication delays
Solution Approach 1:
Each variable frequency drive performs self-regulation through its own speed droop module and flux share module, without relying on external commands from a master controller. This autonomous operation eliminates communication delays and achieves immediate dynamic response to load changes.
Data Source
AI summary
A method for controlling at least two variable frequency drives connected in parallel. The method comprises, for each variable frequency drive, communicating a magnetizing current component value to a master controller, and receiving a speed demand, a flux demand, and an average magnetizing current component value from the master controller. The method also comprises determining a motor speed and a motor flux based on measurements of a stator voltage and current of a motor coupled to the variable frequency drive, determining a speed reference based on a torque current component value, and determining a flux reference based on the magnetizing current component value and the average magnetizing current component value. The method further comprises adjusting a torque current component based on the speed reference and/or adjusting a magnetizing current component based on the flux reference.